There are three different ways to add an item to your plan.
From Tree View
A. Click the '+' in the bottom right hand corner of an existing plan item. This will create a supporting item underneath the existing item.
B. Alternatively, click and drag a Level from the Item Library and drag it onto an existing item (such as the top plan card). This will create a supporting item underneath the existing item.
From List View
A. Hover over an existing item in the plan. Click the 'Add Supporting Item icon' to add an item underneath the existing item.
If you do not see the Add button in Tree View, or the Add Supporting Items icon in List View, it is because you do not have the correct permissions to add a supporting item. Contact your AchieveIt administrator if this is the case.